The book "4D Study of Thoracic Cancer Radiation Treatment" offers a comprehensive analysis of the challenges associated with radiation therapy for thoracic tumors, particularly concerning tumor movement during breathing. It introduces the concept of four-dimensional (4D) radiation therapy, developed to address the issues of tumor motion. Authors TzungChi Huang and Geoffrey Zhang explain the application of deformable image registration, specifically the optical flow method (OFM), for precise dose mapping across different phases of respiration. The book discusses the validation of a dose mapping program and demonstrates its application in tracking radiation therapy. By calculating deformation matrices between 4D CT data and subsequently mapping doses to a unified image, an innovative approach to improving radiation therapy is presented. Additionally, several clinical case studies are showcased to illustrate the effectiveness of the proposed method.